The 3rd Generation Partnership Project (3GPP) was established to produce globally applicable technical specifications and technical reports for a 3rd generation mobile system based on evolved Global System for Mobile communications (GSM) core networks and the radio access technologies that they support (i.e., Universal Terrestrial Radio Access (UTRA) in both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes). The scope was subsequently amended to include the maintenance and development of the GSM technical specifications and technical reports including evolved radio access technologies (e.g., General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)).
In the 3GPP Long Term Evolution (LTE) specification, when operating in multi-user multiple-input multiple-output (MU-MIMO) mode, the scheduler of an evolved Node B (eNB) needs channel quality indicators (CQIs) from the multiple different user equipments (UEs) to make scheduling decisions. Conventionally, CQIs are generated at the UEs and transmitted to the eNB. When a wireless system is operated in single-user multiple-input multiple-output (SU-MIMO) mode, the CQIs can be accurately calculated by the UEs because the UEs have all of the information necessary to calculate the CQIs, which includes the equivalent channel matrix, the usage scheme of each spatial sub-channel, and the inter-cell interference plus additive noise. However, when operating in MU-MIMO mode, the UEs do not necessarily know the usage scheme (pre-coding) that will be used in the next transmission time interval (TTI) for each spatial sub-channel. In MU-MIMO mode, different spatial sub-channel usage schemes will result in different intra-cell interference and consequently different CQIs. In order to account for the different spatial sub-channel usage schemes that could be used and to take full advantage of multi-user scheduling, the UE would need to calculate different CQIs for each different spatial sub-channel usage scheme and then provide the different CQIs to the eNB through uplink signaling. A drawback to calculating multiple different CQIs at each UE and transmitting the multiple different CQIs to the eNB is that these operations consume valuable UE processing and uplink signaling resources.